As known in the paper industry, a variety of types of machines and processes are used for making handkerchiefs, paper towels, and the like, in packages of interfolded sheets of a certain stack height.
Sheets of this type are obtained by stacking the sheets in an “interfolded” way, i.e., at each fold a wing of the previous sheet and a wing of the next sheet engage with each other. This way, when drawing a sheet from the package, a wing of the next sheet protrudes with subsequent practical employment for certain types of users. Among the possible interfolding ways the L, Z or W interfolded sheets are known respectively, with 2, 3 and 4 folds per sheet.
A particularly critical step of the process for production of packages of interfolded sheets, is separating a stack from the next one, once a predetermined height of the pack has been achieved. In the paper industry, high speed working is necessary during the whole production process, and the step of separating successive stacks of sheets represents a critical point of the whole process since it needs a succession of operations that unavoidably slows down productivity.
For this reason, solutions are looked for to provide high speed separating of the stacks.
The different existing apparatus all have a couple of folding rollers that supply the interfolded sheets on a table, and in some cases, a plurality of “folding arms” that go in and out special grooves made in the folding rollers, which forms a stack of interfolded sheets on the table.
In U.S. Pat. No. 4,770,402, when the stack of sheets present on the table reaches a certain height, a first series of means of separation moves into the stack from a side whereas a second plurality moves into the stack from the opposite side, and both for all its width. This way, a pack is separated from the next one, and the pack of predetermined height is precisely arranged between the table and the first series of means of separation. Whereas the other series of means of separation, supports the pack being formed up to the moment when the table comes back. The latter, in fact, leaves the pack with the predetermined height on a conveyor belt and moves back in the stack receiving position for receiving the pack.
These machines have, however, different drawbacks which are caused by the shape and the way of operating the means of separation.
Interfolded products also exist in which the sheets are connected through weak uncut portions, to assist the operation of the interfolding machine. The problem is that in separating two packages it causes tearing of such connections that would keep together two sheets of different packs.
Furthermore, the known interfolding machines can provide a single interfolded configuration, i.e., a single type of fold, and for this reason they have a process with little flexibility. In fact, for a determined type of interfolded product it is necessary to arrange the interfolding machine in such a configuration that its different separating and folding elements are arranged in appropriate relative positions in order to follow a determined succession of steps during the production process.